Polymer blends of ethylene-propylene (EP) polymers or of ethylene-propylene-diene (EPDM) polymers with poly-.alpha.-monoolefin polymers, particularly with polyethylene, are known to the art (see U.S. Pat. Nos. 3,176,052; 3,220,966; 3,303,150; 3,328,486; 3,358,053; 3,751,521; 3,835,201; 3,887,640; 3,914,342; and 3,919,358, and British Pat. No. 1,208,065 and Canadian Pat. No. 602,151). Such blends are useful to prepare a broad range of molded products such as tubing, toys, and household and automotive items. For many applications, the item must have high structural integrity and good tensile strength. Unfortunately, these polymer blends often exhibit low tensile strengths. To achieve higher tensile strengths, curing or crosslinking agents have been added to such polymer blends to effect chemical changes in the blend (see U.S. Pat. Nos. 3,228,883; 3,256,366; 3,758,643; 3,806,558; and 3,862,106). The polymer blends of the present invention are thermoplastic physical blends of specific EP copolymers and polyethylene (PE) polymers, which blends exhibit unexpectedly superior tensile strengths. No curing or crosslinking agents are used in the polymer blends.